Cases are rare in Maryland, which has high vaccination rates, and officials say the possible case is isolated so far. The child, who was not identified, lives in Baltimore County and is unvaccinated.
The child recently visited Sinai Hospital in northern Baltimore City with measles symptoms, city officials said. The child, who is expected to recover, is now in home isolation, and a test to confirm the virus is pending.
Officials from the state Department of Health and Mental Hygiene and the U.S. Centers for Disease Control and Prevention are helping identify unvaccinated contacts.
There have only been three cases of measles in Maryland in the past five years, none in Baltimore County or city. A 2014-2015 state survey shows about 99.2 percent of kindergartners and 99.4 percent of grade school children were immunized.
Children typically receive a combination vaccine for measles, mumps and rubella, or MMR.
Measles is easily spread when an infected person coughs or sneezes. Symptoms include fever, rash, runny nose and red eyes.
"This may be a false alarm and the patient may not have measles," said Dr. Leana Wen, Baltimore City health commissioner. "However, measles is highly contagious, and out of an abundance of caution, we are treating this as a suspected measles case and taking every necessary precaution to ensure the health and safety of Baltimore residents."
Sinai Hospital said it was coordinating with the health agencies and working to notify workers and visitors in the emergency department the morning of Aug. 6 when the child came in.
"Upon recognition of a possible measles case, Sinai Hospital staff acted quickly to take precautions to reduce exposures," said Sharon Boston, a spokeswoman for Sinai. "Protecting our patients, visitors and employees is our responsibility and highest priority. We are taking appropriate action to ensure the health and safety of all those who may have been in contact with this patient."